Goldschmidt 2012 Conference Abstracts Killed by geochemistry: Mass Super-high atmospheric oxygen levels extinction in toxic oceans during the Great Oxidation Event

1* 1* LEE R. KUMP LEE R. KUMP 1Dept. of Geosciences, Penn State University, University Park, USA, 1Dept. of Geosciences, Penn State University, University Park, USA, [email protected] (* presenting author) [email protected] (* presenting author)

The boundaries between geological periods often mark major losses A combination of geological and isotopic evidence demonstrates of biodiversity, i.e., mass extinctions. Geochemistry is used to that the atmosphere became oxygenated for the first time in Earth investigate these events, both to determine the trigger for the event history roughly 2.5 billion years ago. The proxies for atmospheric (asteroid/comet impact, volcanism) and the event’s cause (abrupt oxygen in the rock record are quite sensitive, though; an atmosphere warming, anoxia, trace metal poisoning, loss of habitat by sea-level sufficiently oxygenated to support animal life may not have been fall, global wildfires, etc.). For the Cretaceous-Paleogene event, established for hundreds of millions of years after this initial rise. although the trigger is well established to be asteroid impact, the kill A new repository of geological information has recently mechanism is less clear, and trace metal poisoning may have played become available, the result of scientific continental drilling in a role. For the end-Permian, evidence for oceanic anoxia and the Fennoscandia (FAR-DEEP). Kilometers of drill core potentially spread of sulfidic waters into the photic zone is widely associated record a detailed history of the path atmospheric oxygenation took with the extinction horizon in marine sedimentary rocks. Detailed through the critical interval from 2.5 to 2.0 billion years ago. studies of the spatio-temporal distribution of geochemical and Preliminary analysis of these cores has revealed an excursion in the isotopic proxies together with numerical simulations of these events carbon isotope composition of the ocean/atmosphere system that is is leading to a clearer picture of the cause and consequence of mass best explained by a massive oxidation of the continental crust. The extinction in Earth history. event terminates a well-known, equally anomalous but oppositely signed carbon isotope excursion that likely reflects a large accumulation of oxygen in the atmosphere from about 2.2 to 2.0 billion years ago. The hypothesis that arises from these observations is that atmospheric oxygen levels built up to levels that may have exceeded modern during the earlier interval, leading to pervasive oxidative weathering of the continental crust, the first in Earth history, and a large consumption of atmospheric oxygen during the termination event. The suggestion that oxygen levels may have exceeded modern levels during the early stages of planetary oxygenation is provocative, but is consistent with singular geologic events that happened at this time, including the generation of natural nuclear reactors resulting from concentration of uranium by oxygenated groundwaters, and the enrichment in the iron content of banded iron formations by oxidative weathering into ore-grade deposits.

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